Growth striations and impurity concentrations in HMCZ silicon crystals

Abstract

The effect of a large transverse magnetic field on growth striations and impurity concentrations in Czochralski (CZ) silicon crystals was studied. Silicon crystals of 125 mm in diameter were pulled in [1 0 0] direction from 30 kg melt. A magnetic induction of B=2000 G was used to suppress melt convection. The crystals were not found to be striation-free: periodic striations, spaced about 42 μm, due to 25/−0.3 rpm cw crystal/crucible rotation in asymmetric radial thermal field were observed. Preferential chemical etching of heavily doped samples was used to delineate the growth striations. The crystal growth rate estimated from the periodic striations was about 1.1 mm/min, somewhat lower than the nominal pull-rate of 1.5 mm/min. Due to suppression of melt convection, the interstitial oxygen concentration was low: 7–11 ppma (New ASTM) in lightly boron-doped material, which is about half of what is found in a comparable CZ crystal grown without the magnetic field. At this low level, little or no precipitation of interstitial oxygen was induced by a high–low–high annealing of 1150°C/1 h–650°C/1 h–1000°C/11 h. The substitutional carbon was measured to be all <0.1 ppma.